SPLA rebels and the Sudanese Government have accused each other of attacks in oil-producing areas in the south, breaking a truce signed last year.

The temporary ceasefire is supposed to last while peace talks continue in neighbouring Kenya.

The negotiations over issues such as sharing oil wealth and the distribution of jobs in the federal civil service are set to resume within the next two weeks.

Some two million people have been killed in 19 years of war between the northern, Muslim government and rebels from the Christian and animist South.

"Government forces supported by militias... are carrying out since 31 December a large-scale attack using tanks and helicopter gunships on our positions... in the Western Upper Nile region," the SPLA said in a statement.

Some 1,500 fighters and helicopter gunships were involved in the offensive south of the city of Bentiu, according to the SPLA.

Army spokesman Mohamed Basher Sulieman in turn accused the rebels of killing three oil workers in the same region.

He said that the SPLA offensive was repulsed.

Conciliatory

On Wednesday, President Omar al-Bashir made his first-ever Independence Day speech in southern Sudan, in the town of Malakal, not far from where the fighting was reported to be going on.

"The peace that we seek... is a peace for all those in both North and South, a peace which ensures the participation of all in the taking of decisions and the sharing of power and wealth," he said to a crowd of some 30,000 people.

President al-Bashir is trying to woo southerners

Correspondents say that he struck a more conciliatory tone than on Sunday, when he said that "peace will come by the gun if it cannot come by dialogue" through a "jihad", or holy war.

Last July, the two sides agreed on the broad outline of a peace deal but the details still have to be worked out.

A referendum on secession will be held in the south in six years and the government has agreed that Sharia, or Islamic law, will not be implemented in the south.

Correspondents say that Mr Bashir's speech in Malakal sounded like the opening shot of a campaign to persuade southerners to vote against secession.